"If a 45-year-old comes to a rational decision to end his life, researches it in the way he does, meticulously, and decides that ... now is the time I wish to end my life, they should be supported. And we did support him in that," he said.

Life fell apart after wife's death in quarry

Mr Brayley, who had a high-paying job in the oil and gas industry, was not an obvious euthanasia candidate.

But his friends Kerry and Trish O'Neil could see Mr Brayley's life spiralling out of control after the death of his wife Lina, who died at a local quarry in 2011 in what was at first thought to be an accident.

The fact he was so insightful in his decision to make this choice indicates to me that he was indeed a person who had not lost capacity.

Philip Nitschke

The case was upgraded to a murder inquiry, and while police never named Mr Brayley as a suspect, he told the O'Neils the investigation and the loss of his job had made him depressed.

In the weeks before his death he told Dr Nitschke that he planned to take his own life.

"We had a lot of communication with Nigel, he'd been in touch with us for a while, he'd joined the organisation," Dr Nitschke said.

"When I went over to Perth he came along to the workshop, I had a talk to him.

"He was younger than the usual age, we have the usual age of 50. He came at a younger age, I think he was 45."

Nitschke 'had duty to recommend psychiatric help'

Mr O'Neil said he was "horrified" when he looked at his friend's computer and found the exchange of emails with Dr Nitschke.

He believes Dr Nitschke, who founded euthanasia group Exit International, had a duty of care to recommend psychiatric help.

"I would've expected Dr Nitschke to be coming back and saying, 'Look, you don't fit within the ambit of Exit members; you're not a terminally ill person, you need to seek counselling, assistance, family support'," he said.

"But that wasn't done."

Dr Nitschke says it was not his job to do that, and says Mr Brayley was of sound mind when he made the decision to die.

"If a person comes along and says to me that they've made a rational decision to end their life in two weeks, I don't go along and say 'Oh have you made a rational decision? Do you think you better think about it? Why don't you go off and have a counsellor come along and talk to you?'' he said.

"We don't do that.

"If a person is so depressed that they have lost capacity, then they can't articulate anything," he added.

"The fact that he was so insightful in his decision to make this choice indicates to me that he was indeed a person who had not lost capacity.

"I'm not saying he wasn't depressed but was he so depressed that we should constrain him? Should we have certified him, should we have put him into a psychiatric institution, should we have restricted him in some way?"

Dr Nitschke said Mr Brayley was "not at that level" and "people like that should not have their freedom curtailed".

"I would object to that idea, you are saying he's depressed therefore we shouldn't talk to him. Everyone is depressed at times, and at this time this person fit that criteria."

But Mr O'Neil believes Dr Nitschke's organisation has moved into uncharted territory.

"I think most people would assume [Exit International's] role is quite clearly for people who are terminally ill, suffering, reaching the end of their life," he said.

"Not for people who are going through a down period in their life, everyone goes through a down period in their life."

Beyond Blue chairman Jeff Kennett said Mr Brayley was not a euthanasia candidate.